Electron tube with high ohmic wall coatings



June 13, 1939. SCHWARTZ ET AL 2,162,391

ELECTRON TUBE WITH HIGH OHMIC WALL COATINGS Filed Apyil 15, 1956 COL LO/DAL HIGH RES/S TANCE COATING INVENTORS,

ER/CH SCHWARTZ Y KURT WELLMANN B WTTORNEYS.

Patented June 13, 1939 UNITED ST T S ELECTRON TUBE WITH HIGH OIIMIO WALL COATINGS Erich Schwartz and Kurt Wellmann, lemon-- dorl, near Berlin, Germany, alsignors to the firm or Fennel: Aktlengelellachait. Zehlendorl, near Berlin; Germany Application April 18, 1936, Serial No. 74,222 In Germany April 18, 1935 Claims. (or. 250-102) The present invention relates to television transmitting and receiving tubes, oscillograph tubes and similar discharge tubes having a conducting coating on the inside wall of the tube.

5 For various purposes, e. 3., in the case of supplementarily accelerated Braun tubes or accelerating lenses of low refractive power but consequently high potential power, it may be desirable rial practically constitutes a short circuit; ii the concentration is too high, the resmtance rises too rapidly, and right within the range of resistance Values which such layers must have, the concentration-resistance curve runs ofi in very steep fashion.

In the drawing, the figure illustrates a common type of cathode ray tube including ahigli resistance coating on the inner wall thereof.

The tube I has a viewing screen 3 at one end,

an electron gun 5 at the other end. and the as.

tomary intermediate electrodes such as the control grid 1, anode 8, and deflecting plates i i. A high resistance coating it, to which the invention relates in particular, b formed on the inner wall of the tube.

Experiments have shown that a more positive and convenient result than heretofore is obtained if colloidal non-conductors in suitable concentration are added to the colloidal graphite. The use of waterglass for producing a high resistance becomes thus superfluous, and it is possible to reduce the addition of waterglass to such an extent that merely suflicient adhesion to the wall is produced. Colloidal copper oxide is particularly well adapted as a colloidal non-conductor for this purpose.

It has furthermore been ascertained that colloidal semi-conductors" may easily be prepared which yield a high ohmic resistance of suitable value without admixture with colloidal graphite;

for example, colloidal pyrolusite (MnOz) may be applied to serve as a single component resistance. Such layers produce resistances of 2 to 7 megohms on the inner walls of ordinary tubes. If the conducting values are too low, for special cases, colloidal graphite may be 1 added to such semiconductors," just as it may be added to colloidal non-conductors. Inasmuch as in nearly all applications oi television tubes it is important that the colloidal inner wall be black, it is preferable 5 to select black colored substances in choosing the colloidal material. In this respect also the three substances, copper oxide, pyrolusite, and carbon are particularly suitable.

It is known in transmitting tubes of the Farns- 0 worth type to apply very thin metal layers upon the wall of the tube between the photo-electric electrode and the anode. In such tubes the high-ohmic layer of the invention is of particular advantage. Since caesium is generally used in 15 forming the phdto-cathode, care hitherto had to be taken of the caesium when using metallic wall coatings, since t eilcaesium might become incorporated therewith and thus alter the resistance value. With the semi-conductor coatings of the 20 invention the adhesion afiinity for caesium is appreciably less, so that the resistance value remains constant during the photo-cathode formation process. Flu'thermore the light sensitive eilect remains limited to the cathode surface. In 25 this type of transmitting tubes the absorption of visible light on the inner wall is of importance since the light radiated back from the tube walls would cause a clouding of the transmitted picture. Consequently, the use of black colloids is 30 01' importance also in transmitting tubes.

We claim:

1. In a cathode ray oscillograph comprising an evacuated insulating tube having an electron gun I sistance of said coating. 40

2. In a cathode ray oscillograph comprising an evacuated insulating tube having an electron gun therein and a fluorescent screen disposed in registry therewith, a hiuh resistance coating on the inner surface or said tube between said gun and 45 said screen, said coating comprising a mixture of colloidal manganese dioxide and a. binder.

3. In a cathode ray oscillograph comprising an evacuated insulating tube having an electron gun therein and a fluorescent screen disposed in 50 registry therewith, a high resistance coating covering the inner surface of said tube between said gun and said screen, said coating comprising a mixture of colloidal copper oxide and a binder.

' 4. In a cathode ray oscillograph comprising an 55 evacuated insulating tube having an electron gun therein and a fluorescent screen disposed in registry therewith, a high resistance coating covering the inner surface of said tube between said gun and said screen, said coating comprising a mixture of colloidal copper oxide, colloidal graphite, and a binder.

5. In a cathode ray oscillograph comprising an evacuated insulating tube having an electron gun therein and a fluorescent screen disposed in registry therewith, a high resistance coating on the inner surface of said tube between said gun and said screen, said'coating comprising a mixture of colloidal manganese dioxide, colloidal graphite, and a binder.

6. In a cathode ray oscillograph comprising an evacuated insulating tube having an electron gun therein and a fluorescent screen disposed in registry therewith, a high resistance coating covering the inner surface of said tube between said gun and said screen, said.coating comprising a mixture of material conductive to flow of current, material highly resistant to flow of current, and a binder, said mixture being so proportioned that the conductivity is controlled by said high resistance material and is not controlled by the binder.

"I. In a cathode ray oscillograph having an evacuated insulating tube enclosing an electron gun and a photo-electric screen disposed in registry therewith, a high resistance conducting layer disposed upon the inner surface of said tube between said gun and said photo-electric screen, said layer comprising a mixture of colloidal high resistance substances having a low adhesion afilnity for said photo-electric screen.

8. In a cathode ray oscillograph having an evacuated insulating tube enclosing an electron gun and a photo-electric screen disposed in registry therewith, a high resistance conducting layer disposed upon the inner surface of said tube between said gun and said photo-electric screen, said layer comprising a mixture of colloidal high resistance substances having a low adhesion aifinity for said photo-electric screen, and being non-sensitive to light.

9. In a cathode ray tube comprising an evacuated envelope having therein an electron gun and a screen disposed in registry therewith, and adapted to be impacted by cathode rays, a high resistance coating on the surface of said envelope between said gun and said screen, said ,coating comprising a mixture of colloidal light absorbing material for precluding light reflection, a colloidal high resistance material for controlling the resistance of said mixture, and a binder in sufilcient amount to adhesively secure said mixture to said envelope but insufficient to control the resistance of said mixture.

10. In a cathode ray tube comprising an evacuated envelope having an electron gun and a screen therein, said screen being disposed in registry with said gun and being responsive to cathode ray impact, a 1* 'h resistance coating on the surface of said envelope between said gun and said screen, said coating comprising a mixture of a conductive colloid, a high resistance colloid and a binder, said mixture being so proportioned that the coating conductivity is not controlled by the binder.

ERICH SCHWARTZ. KURT WEIIMANN. 

